The present invention relates to a liquid crystal display. More particularly, it relates to a transflective type liquid crystal display which provides good screen visibility in outdoor use such as under sunlight as well as in indoor use.
Liquid crystal displays, which do not emit light by themselves in principle and display a screen using optical shutter effect caused by polarization, are roughly classified into three types according to the lighting source they use: transmissive type, reflection type, and transflective type.
The transmissive type LCD has a back light at the back as a lighting source. The back light needs to be lit continuously for screen display and the screen cannot be displayed when the back light is off. The reflection type LCD contains a reflective film to reflect external light and displays a screen using the external light as a lighting source. This type has an advantage in that it consumes minimal power because it does not use a back light, but it poses a problem as to how to ensure visibility because display brightness varies with the ambient brightness and the screen can hardly be recognized in dim light during the night. The transflective type LCD has a reflective film which reflects external light. In a bright environment, this type of LCD displays a screen using external light as a lighting source. In a dim environment, it displays a screen using a back light installed at the back.
Thus, the reflective film has apertures for use to pass the back light and the screen is displayed using light from the back light passing through the apertures, as a lighting source. The transflective type LCD, which can reduce power consumption using external light and make a screen easily recognizable even in a bright ambient environment in the daytime, is suitable, in particular, for mobile terminal devices such as cell phones, of which power savings are required. However, since this type has apertures in the reflective film and switches between external light and back light depending on the situation, the visibility of the screen varies between the two lighting sources—external light and back light—depending on the area of the apertures. There is a trade-off between the two lighting sources, with results in decreased visibility in both reflective display and transmissive display. The light from the back light, in particular, is blocked by that part of the reflective film where there are no apertures, resulting in decreased brightness.
To deal with this situation, Japanese Patent Laid-Open Publication Nos. 2003-84276 and 2003-255318 disclose techniques for increasing screen brightness during the use of an internal lighting source by focusing the light from a back light onto the apertures using microlenses while increasing screen brightness during the use of external light by reducing the area of the apertures in the reflective film. Also, Japanese Patent Laid-Open Publication Nos. 2001-116917 and 2003-121612 disclose methods for manufacturing an optical part equipped with microlenses.